Shape Description by a Syntactic Pyramidal Approach

In the syntactic approach to pattern recognition, patterns are represented as strings, where each pattern is expressed as a composition of its component patterns, called subpatterns and pattern primitives. This approach draws an analogy between the structure of patterns and the syntax of a language. The patterns are considered at a single resolution level, and the recognition of each pattern is usually made by parsing the pattern structure according to a given set of syntax rules, obtained in the first stage of the analysis. This paper describes a pyramidal approach to 2-D object representation which relies on a linguistic description of the object contour at different resolution levels. Our approach, which is parallel and context-sensitive, implies the use of higher dimensional grammars for defining production rules which describe the evolution of the contour between levels. This method is computationally efficient (due to the fast coarse-fine search), rotationally invariant, as well as rather insensitive to noise.